Circuit breaker latch mechanism



March 10, 1953 0. M. UMPHREY 2,631,199

CIRCUIT BREAKER LATCH MECHANISM Filed April 17, 1950 2 SHEETS-SHEET 2 I INVENTORT DONALD M. UMPHREY.

WrSW

ATTORNEYS.

II I I [III III I l II/II I II I I III/Jj tacts. ally or in response to an overload or fault cur- Patented Mar. 10, 1953 CIRCUIT BREAKER LATCH MECHANISM Donald M. Umphrey, Palo Alto, Calif., assignor to Pacific Electric Manufacturing Corp., a corporation of California Application April 17, 1950, Serial No. 156,410

8 Claims.

This invention relates to mechanisms for actuating circuit breakers, and while it is particularly applicable to circuit breakers of the largest size, as utilized for breaking high voltage circuits of large power-carrying capacity, it is also applicable to breakers of smaller types.

Among the objects of this invention are to provide a mechanism which will close a circuit breaker quickly and positively upon the application of either a local or remote control, to provide a mechanism wherein the break can be accomplished with extreme rapidity, i. e., in from one and one-half to two cycles following the application of a fault current of sufficient magnitude to cause the breaker to trip instead of requiring three cycles as is the case in more conventional breakers, to provide a mechanism which will trip free of the closing mechanism and break the circuit with substantially equal speed and positiveness in case a short circuit or other fault is either already present or occurs at the instant when the breaker is being closed, to provide a circuit breaker which will operate without failure if an attempt is made to reclose it while the fault still exists, to provide a circuit breaker mechanism employing a latching mechanism of the toggle type having a large mechanical advantage, but

- which has, at the same time, a minimum effective inertia, and, generally, to provide a circuit breaker mechanism of maximum reliability and simplicity.

The operating mechanism of this invention may be used in substantially any of the known types of circuit breakers, which, generally speaking,

comprise one or more stationary contacts which are engageable by one or more moveable con- Trip mechanisms, operable either manurent, release means to separate the stationary and movable contacts, the separation usually being accomplished by means of a powerful spring in order that the circuit may be broken as rapidly as possible.

The equipment which is the subject of the present invention is for the purpose of closing the breaker against the action of the spring and includes the latch and trip elements referred to. Broadly speaking it comprises a source of hydraulic pressure, preferably a high-pressure pump plus a hydraulic accumulator. The latter may be of the type comprising a chamber to which the pump is connected, which chamber contains a bag or balloon containing, preferably, an inert gas such as nitrogen and formed of oilresistant synthetic rubber or elastomer such as neoprene, since the actuating fluid is frequently an oil. By the use of the accumulator the primary pressure source may be a high pressure pump of small capacity, the normal function of which is merely to maintain the proper pressure in the accumulator which acts as a secondary pressure source. I

The operating element for compressing the opening spring and thus closing the circuit breaker comprises a hydraulic cylinder and piston, the cylinder being connected by a conduit system both to the pressure source and to a sump into which the cylinder discharges the fluid contained therein when the circuit breaker opens, the fluid thus discharged being recirculated back to the accumulator. A hydraulically-operated valve in the conduit system connects the cylinder alternatively to the pressure source or, through an exit port, to the sump, this valve being so constructed that when hydraulic pressure is applied thereto it operates first to cut off. the passage from the cylinder to the sump and then to open the conduit from the pressure source into the cylinder and thus operate the piston,

Where a breaker of the type here under'consideration is used it is obvious that the possibility always exists that an attempt may be made ,to close it when a fault, such as a short circuit, exists on the line which it feeds. When this occurs it is important that the breaker should trip open as positively and substantially as rapidly as would be the case if the fault occurred with the breaker in its latched-closed condition and no hydraulic pressure applied thereto. This is particularly the casein self-reclosing circuit breakers which are designed to attempt to re-close the circuit automatically one or more times after a fault occurs, in the hope that such fault may be'of a purely transient nature which will clear itself.

The mechanism for actuating the main valve while permitting the breaker to trip free when closed under a faulty line condition comprises a pilot valve interposed in a connection from the pressure source to the hydraulically-operated main valve and a dump valve which normally closes a bypass to the sump positioned between the pilot valve and the main valve, the dump valve being so constructed that it tends to open when pressure is applied through the pilot valve to the main valve line but is normally'prevented from operating in response to such pressure by mechanical means which may be disabled by the operation of trip mechanism operating coordinately with the trip of the latch holding the circuit breaker closed. i. 'r :1?

The pilot valve, besides controlling the application of pressure from the source to the main valve, is preferably operated by pressure from the same source. It is, however, externally operable either by direct manual or by remote control. In its preferred form the pilot valve comprises a moveable valve element which, when subjected to pressure on one side, tends to close the pilot valve and when subject to pressure on the other side tends to open it, the area exposed to the closing pressure being greater than that exposed to the opening pressure sothat when pressure is applied to bothsides the valve tends to remain closed. The pressure is applied continuously and at full force to the side which tends to open the valve, but there is a leak or highresistance passage to the closing'side. Accordingly, under static conditions when there isno flow from the pressure. source, the hydrostatic pressure on the two sides of the valve equalizes ..;an'd; because bijthe larger area-tendingto close litheiv'jalvei it remains tightly shut.

it passagewayleads fromthe closing side-of the valve element, into the sump, this passage being normally .blockedby an auxiliary valve which can be externally operated-to actuate the mechanism. When this latter-valve'is opened the'pres- :sureter'iding to hold thevalve closed-is relieved "aandthepilotvalve at once opens, 'actuatingthe .main'valve' and closing the circuit breaker. If, however, the-"triptis' actuated while this condition i obtaihs the dump valve-operates, relieving the "pressure-both upon the main va-lve'and the open- '-ingt;side:of the pilot valve element, the latter :"closes-andthebreaker trips free. Such process -isispeededand made more positive by the fact "that the operation ofthe dump valve also'closes the passage into the sump from the closing side "of the pilot valve, permitting the pressure to build up-and, what is equally important, prevent- -'-ingthe wasting of oil from the pressure source "into'thesump.

The; pressures used within the mechanism to operate the various valves are preferably high- I oftheorder of a fewthousand pounds per square --inch-. To withstand these pressures the various "parts of the valves are necessarily sturdy but their actual sizes are not large and their masses arerelatively small. It will have been noted from the-foreg-oing general description that differential pressures operate throughout and, as will be seen -in-the more detailed description which follows, the-areas overwhich 'these'pressures act are so computed that even the diiierential'pressures are lame and, acting upon the relatively small 'masses of' the moving arts,- operate them with extreme rapidity; Speed of operation is, of course, of primary importance in circuit breakers. In order to obmm high operating speeds high rates'of accelera- 'tion "are necessary, which'means either that the masses-moved must be small, their velocities mustzbe small-or the actuating forces must be large. In high: power circuit breakers the breakr .ingz'mechanisms themselves'have to be sturdy and -to move throughconsiderable distances and since thisinvolves .aconsiderable mass, large opx-erating. forces, i..e., powerful springs, are required, .and this in turn necessitates that large forces be used to compress (or extend) the springs, '1 In "the past either mechanical methods havesbeenr used tov close the circuit. breakersor, -alternatively, pneumatic methods. The forces 'ausedto trip. the circuit breakers, however, must be relatively small since these devices should. be

surface, quite attractive and hydraulic methods have not been generally used because of the greater masses which must be moved. A careful examination of the problem, however, develops the fact that because of the compressibility of asesand theirnecessity of expanding into the operating cylinders or other equivalent chambers where they canexert their forces, a material lag isintroduced in pneumatic devices. No such time for expansion is necessary when hydraulic actuationwislused. .Changes in pressure are propagated between control valves and any mechanism which such valves operate with the speed of sound in the medium which may well be several through which the, pressure acts. may. be made short-and the. friction. losses..correspondinglywlow so that much quicker operationmay beachieyed through hydraulic .mea-ns; than through pneumatic.

. Pneumatic breakers. are,-moreover, subject to a: number of disdavantages which do, not. at first "appear. iGasesxare' hard .to retain, leaks readily occur and tarehardrto detect, andtherefore closed pneumatic"systemsarenot used. 'With an open pneumatic system losses, due to leakageor to the releaseof 'gas-when-the pressure rises above the desiredlimitxdue to'ex-pansion from changing temperature: are supplied from. the surrounding air by a pump: which is electrically drivenunder the control of.-an .electricallyeoperated switch.

There .is also,.in such "cases, inevitably-a lossrof compressed air every time. thatthe breaker is actuated, which: loss must also-be made up by the pump. .The: power required for'make-upof this vcharacter, is not particularly important, but what isimportantisthe fact that the air. tobecompressed always contains some water. vapor and almost always is contaminatedby carbon dioxide,

' sulphur dioxide, and frequently other even more corrosive.- materials. The water vapor condenses in the receiver of the system andmust be blown .out from-time-to time. 'It is always carried, to

some-extent, into-the connecting lines and valves. Corrosion always takes place within theair receiverand frequently. *Withinthe control valves. -Particles-of-rust or other corrosionproducts may I be, carried through the: air-passages .oithe system into, the yalvescausing, them .to stick,- and .ubecause-oflthe, chances ,of actual perforation of the. receivers or the pipes connecting the latter vwithzthe operating mechanism thewhole. device must- .be subject to constant, inspection. Therefore, although the. pneumatic operatingsystem may .be simpler and lighteriin weightthan .the

-mechanical-system and cheaper, than a hydraulic system in first cost, it is, in the long run. more expensive. and less reliable as well as slower in =operation than the hydraulic system which is'the subject of this application.

The above considerations" may be more fully appreciated, and theinvention and itsvarious objects and advantagesmore fully understood, from the following detailed description of a preferred embodiment thereof, taken in connection with the accompanying drawings. wherein:

the invention;

Fig. 2 is a sectional view of the closing, latching and release mechanism of such a breaker, the accumulator and main valve mechanism being shown, for the purposes of illustration, as being rotated 120 degrees from their actual position 1n order that the entire operating mechanism may be illustrated in a single diagram; and

Fig. 3 is a schematic circuit diagram of the electrical portion of the trip mechanism.

Figure l is a schematic diagram of one form of circuit breaker which may be operated by the subject mechanism of this invention. The type of breaker shown is merely illustrative since the invention may be modified to actuate almost any of the known types of breaker, of which there are many. In the figure the block A represents the mechanism more fully illustrated in Figure 2, the projecting plunger I representing the operating member which is driven downward hydraulically in order to close the breaker contact. The plunger connects through a link 3 to a bell crank 5, the bell crank in turn operat ng a pull rod 1 which moves towards the left of the diagram and compresses an opening spring 9 when the plunger is retracted or pulled downward. Bell crank 5 and pull rod 1 are mounted upon a suitable supporting framework Pivoted to the frame I and the pull rod 1 is a parallel motion linkage |3 of known type to which is connected a vertical bar IS. A transverse drop bar l7, carrying the movable contacts of the breaker, is secured to the lower end of the bar H3. The latter, as well as the pull rod 1, is preferably made of insulating material such as impregnated wood, porcelain, Bakelite, or other material having the requisite dielectric strength. When in the closed position shown in the dia-- gram the moving contacts carried by the drop bar make contact with fixed contacts IS in the transmission line 2|! which is to be controlled by the breaker. Connection between the fixed and movable contacts is made within interrupter structures 2| for extinguishing the arc. Fixed contacts, moving contacts, and interrupter are all preferably immersed in oi1 or other arcquenching dielectric liquid within a tank 22.

Means are provided for tripping the breaker, either manually or in response to an overload, such means comprising, for example, a current transformer 23 in the line 29 which actuates a marginal relay 24, closing the relay contacts and completing a circuit, including a storage battery 25, to the trip mechanism of the breaker which will be described later. Alternatively the trip circuit may be actuated by closing a manuallyoperated switch or key 21.

As has been indicated, all of the parts referred to, with the exception of the mechanism A itself, are well-known in the art and might be taken for granted, but are shown here for the sake of completeness. It is to be noted that the one mechanism may operate a number of drop bar elements, for example, one set in each leg of a threephase line. Under other circumstances separate mechanisms may be used in each phase so that if a fault occurs in one line only that particular line may be deenergized and the load carried, at least in part, by the other two phases. All such expedients are well known and need not be further considered here.

The block A of Fig. 1 represents a tank-like housing within which the actual operating mechanism is encased. Within this housing is a highpressure motor-driven pump P, controlled by a pressure-actuated switch, which develops the hydraulic pressures for operating the device. The pump P withdraws hydraulic fluid from a tank or sump 28 and delivers it to the accumulator through a conduit 29. For protection against excess pressures a by-pass 30, controlled by a relief valve (not shown) returns excess fluid to the sump.

The hydraulic operating mechanism itself is preferably mounted on and (in part) encased within a base block 3| which may conveniently be a single casting. The bottom of this casting is bored or otherwise recessed to form a hydraulic cylinder generally indicated by the reference character 33, the cylinder being provided with a steel liner 35 of high tensile strength material to withstand the hydraulic pressures used. Within the cylinder a piston 31 is mounted on a piston rod 39 to which the breaker mechanism is connected through a linkage which will be described in detail later. Suitable means are used for sealing the piston against the hydraulic pressure which it is required to bear, a preferred means being a seal comprising a ring 4|, of neoprene or other oil-resisting synthetic rubber, Within a groove 43 formed in the periphery of the piston. A conduit 45 opens axially from the top of the cylinder 33; if the baseblock 3| is cast the conduit may be cored in the casting. Piston rod 39 runs through the axial opening into the cylinder, this port being of ample size to admit the oil or other hydraulic fluid around the piston rod. Above where the conduit 45 opens into the cylinder the block is accurately machined to size to form a bearing for the rod and a ring seal 41 is provided to prevent leaking of the hydraulic fluid around the piston rod.

The baseblock 3| is provided with a bore or other accurately-sized opening, whose axis is parallel to that of the cylinder 33, for receiving a main valve housing 49, the bore intersecting the conduit 45 and also an exhaust conduit 5| which opens into the sump 52 in which almost the entire baseblock 3| is submerged.

The main valve housing 49 is accurately fitted within its bore in block 3| and for additional security against leakage is provided with ring seals. At its upper end it carries, upon a flanged bushing 53, an accumulator reservoir 55, seals again being provided to prevent loss of pressure around the bushing and past the flange. The accumulator opens, through channel 56 through the bushing into the interior of the generally cylindrical main valve housing 49. A centrally ported septum 5'! partially closes the housing 49 above the conduit 45, a conical poppet-valve seat being formed in the upper side of the port through the septum.

Above the septum the housing is provided with ports 59, one of these ports leading through a high pressure pipe or other connection 29 to the outlet of the high-pressure pump P; the other port leads through a similar connection (which may be bored or cored in the block 3|) to the pilot and dump-valve mechanism which will later be described, this second connection being indicated schematically as a pipe 6|. These connections are open at all times.

A poppet-valve 63 is seated in septum 51. This valve has a cylindrical section 65 rising above its conical valve face and terminating in a flange which slides in and is guided by the valve housing 49. A spring 69 bears against the upper portion of this flange, tending to keep the valve seated. This cylindrical portion of the valve is provided with ports 1| to permit the :flow or .liquld, past the .fiange andthroughv the septum portintothe lower. body of the housing when thevalveis .openaswell asto permit the flow; of oil. into and-out of the accumulator through the ports 59. The stem of the poppet- .valve 63 is of relatively large. size and isprovided with a longitudinal channel 13' there- -through, and; has an enlarged foot 15.

"I'heioot 15 fits within a recess f ormedin the top of-a floating. valvepiston TI and. is provided witha ring sealwhich prevents leakage through the stem and recess.

.Below the septum, 51 the housing 49 is supplied withports .19 connecting to the'conduit 45. B low. t ese p t again, theo e i s it in t e ous n nla s d s ie y t rm he mation of. a. conical. valve-face 8] between the portionoi' the housing connection to the. conduit-=45 and its lower-most portion which forms a cylinder within which the valve-piston 11 slides. Immediately below the valve-face 8! ports 83-open into.the discharge conduit 5l and the sump.

Thelower end. of the housing 49 .is closed by a sealed plug85 uponv which the valve-piston rests when inv its lower-most position. Piston TI, is generally cylindrical, and is sized toan easily sliding fit within the cylinder formed by the lower portion of the valve housing. At its upper end, however, there is a portion of reduced diameter to form ashoulder 81 which forms a valve face seating against the valve-face 8| when the piston is in its raised position. Above the-shoulder 81 the piston is sized to a sliding fit within the housing bore,-so that as the piston rises it closes ofithe passage to the conduit 51 sufliciently well .to prevent. the escape of any material amount othydra-ulic fluid even under the-pressures applied fromabove until the conical faces BI and. 81; engage. and complete a tight seal.

The lowerend of the piston has formed within it a recess or counterbore 89. The outer diameter of the. piston is alsosomewhat reduced at the lower end to form a channel. 90 surrounding it, and a small notch 9| in the bottom of the piston connects-this channel with the recess 89 to admit an initial flowof fluidthereto when, pressure is applied. Channel. 90 connects through port 92 in the housing 49 through a lead schematically indicated as a pipe 93 to pilot valve mechanism through which pressure for operating the mechanism issupplied.

It will be seenthat when the valve piston 11 s i th o i i n. w p p alv is he .c1os d.. t by t ehydra li r ss e r the accumulator" and the spring 55. The efiective area thrqugh which this pressure is applied is it very rapidly until the piston strikes the foot 15 of the poppet-valve.

The parts are so proportioned that this occurs at the same instant that the reduced upper end of the piston enters the smaller bore above it and closes off the connection between the conduit 45 and the discharge conduit intothe sump. At this instant the pi ton. r s to r i h r nn a a so. ope

,fingitdully whenthe valve faces 81 and Bi engage a d itting the ,full hydraulic pressure from the accumulator to the conduit Y 15. and to the cylinder 33, thereby forcing the piston 31 down to the position shown in the drawing, and closing the breaker. At no time is the area upon which the operating pressure acts to force the main valve piston 'I'I downward greater than that referable to the reduced diameter of the upper portion of the piston, while the area below piston 11 is always equal to the full piston diameter and istherefore enough greater to cause positive operation of the valve.

When the pressure below the Valve-piston H is relieved, however, the pressure from above it immediately forces it downward with the result that the poppet-valve 63 first closes, and the passage from the conduit 45 into the discharge conduit 5| next opens relieving oil pressure upon the operating-piston 3'! so that the circuit breaker may open'uncler-the full force of the spring 9 and without being subjected to any material retarding force from the hydraulic system during the major portion of'its stroke. As the stroke approaches its end, however, an enlarged portion 39' of the piston rod enters the port into channel 45, restricting the flow of liquid and bringing the mechanism to rest without excessive shock.

It is to be noted that hydraulic pressure within thecylinder 33 is not relied upon to hold the circuit breaker in the operative position; instead a latch mechanism is provided together with means for relieving the pressure beneath the valve-piston Tl as soon as the closing operation is complete. The means for accomplishing this will next be described, first the hydraulic pilot and dump valves, finally the latching and tripping mechanism.

Both of the latter two valves are mounted in bores formed within a-block 95 which may either be integral with the block 3| or may be separate and secured thereto. The pilot valve bore consists of a lower portion 975 of minimum diameter which connects, through a coupling 93 and a suitablehydraulic conduit 93 already mentioned, with the port 92 in the main valve cylinder. Above the portion 9? is a cylindrical bore HM of somewhat larger diameter which connects with the bore 9'! through a conical valve seat 133. The lower portion. of the bore lill communicates directly through the schematically indicated connection El and the port 59 with the high pressure source.

A loosely fitting piston m5 slides within the bore IDI. No seals are provided for this piston,

.asit is intended to have the high pressure hydraulic fluid leak past it. The piston 5 has at its lower end'a-reduced portion terminating in a valveface engaging the valve seat I653 and forming, above it, a shoulder immediately above the port into thecylinder from the connection 64.

Hydraulic pressure from the accumulator there- .fore. operates against this shoulder and tends to raise the piston andopen the passage from the connection 6| into the passage 93 and the main valve piston. Normally, however, this pressure is more than counterbalanced by pressure from the hydraulic fluid flowing past the piston and operating against the full area thereof, thus tending 7 ll. Theneedle valve may, however, he externally operated either by manipulationof a handle l lii vor, by rernotecontrol through the lever- H5 and a solenoid II! (which is schematically indicated) or by other suitable means.

' A dump valve bore is formed in the block 95 parallel to the pilot valve bore and two connections exist between the two bores. The first of these connections passes through the valve block I81 and connects the bores above the needle valve. The second of the two connections is below the valve I03.

Like the pilot valve bore, the dump valve bore has a minimum diameter portion I I9 at its lower end, this portion opening above into a valve-cylinder portion of somewhat larger diameter and below into the sump. A tubular piston I23 slides within the cylinder. The lower end of the piston is reduced in diameter to form a sliding fit within the bore H9, forming a shoulder I2! above the reduced portion, and the passage I23 from the outlet of the pilot valve enters the dump valve bore below the shoulder, so that when the pilot valve is open pressure is applied beneath the shoulder tending to raise the piston and open the dump valve. The upper end of the piston is supplied with a flange I23 which limits its downward motion and, when the valve is closed, lies within an annular channel communicating through the connection I3I with the outlet side of the needle valve I09. Above the flange I29 the piston is provided with extension lugs I33 which bear against a flange I35 on a pushrod I3I.

The push rod I3! slides in a ring-sealed bearing in a cap I39 which fits into the upper end of the dump valve bore. A compression spring MI located within a recess in this cap bears against the flange I35 and thus tends to hold the valve piston I23 in its lower position and close the passage between the pilot valve bore and the sump. Moreover, during the interval when the breaker is being closed, the push rod is normally mechanically locked in this position unless the breaker trips. As will be seen from the drawing, when the dump valve is closed a passage exists from the channel I3I between the lugs I33 and down through the hollow center of the piston into the sump. When the piston rises, however, the flange I29 enters a closelyfitting portion of the bore above the channel and closes off this passage.

Turning now to the more purely mechanical parts of the apparatus including the latch and trip mechanism, the piston rod 39 connects to the breaker plunger I through a strut I59. A compression link I5I is hinged at one end to the strut; its other end is pivoted to one arm I53 of a bell crank which is so mounted that when the switch is in a closed position, as shown, the arm makes approximately a 45-degree angle with the axis of the piston rod 39. As the breaker opens and the piston rises the axis X, about which the link I5I turns, moves up into the position indicated in the drawing by the point X. The link I 5| swings in a counterclockwise direction during this motion, moving the bell crank in a counterclockwise direction up to the point at which the link is horizontal, after which it reverses the bell crank motion, moving it very slightly clockwise and bringing it to rest at an angle of between ten and fifteen degrees from the vertical. At this point the other arm I53 of the bell crank is approximately horizontal.

It is the aim in all circuit-breaker design to separate the breaker contacts and open the circuit as rapidly as is possible. In high-power breakers the necessity of opening a wide gap to insure rupture of the arc, of large insulating members to withstand the high voltages employed, and of relatively heavy conductors to carry the currents involved require that rather heavy masses be moved. To move such masses rapidly requires very large accelerations and a spring of great power. Trip mechanisms used to release such breakers must, however, be sensitive; i. e., small tripping forces must be used to control heavy springs. In order that this may be done, the actual latch mechanism must be given a very great mechanical advantage with respect to the spring. The inevitable result of this is that an equal mechanical advantage is given to the inertia of the latch itself. At the instant of its release the velocity of the latch bears the same ratio to the velocity of the switch mechanism itself as the ratio of the mechanical advantage which the latch possesses, and since inertial effects vary as the square of the velocity the limitation upon the opening time of the breaker is usually the inertia of the latch.

This disadvantage may be minimized by using a linkage system in which the mechanical advantages change rapidly as soon as any motion takes place. Such a system is a toggle formed of compression links; theoretically, the mechanical advantage of such a system varies between infinity when the toggle links are perfectly straight to zero when the links are fully buckled. In practice, however, no such wide range is possible, since at the position of infinite advantage the linkage is unstable and slight mechanical inaccuracies may prevent its operating in the manner intended. Gains up to a maximum of from (say) 8 to 15-fold may be obtained with a toggle linkage without incurring instability, or requiring undue accuracy of machining or adjustment.

The theory of the rapid change of mechanica advantage in a toggle link system is that the lever arm through which the restrained force acts to buckle the links when the toggle is released increases rapidly. The use of this principle in latching mechanism is old per se. In the present mechanism, however, this effect is multiplied by two expedients; first, a plurality of toggle linkages is used in cascade, and, second, compound toggle linkages are used where in the force which is used to buckle the originally nearly straight toggle links is itself applied through a pair of links which are buckled at the start of the action but which straighten as the latching links buckle. Through this latter expedient the mechanical advantage is very rapidly transferred from the latch mechanism to the breaker and breaker spring with the result that the inertial load of the latch is dropped still more rapidly and the motion of the latch mechanism itself becomes very small in spite of its initial mechanical advantage. The transfer of inertia, as regards the final links of the series may, in fact, be made so rapid, that it is only at the initial instant of the trip that it contributes to the inertia, its velocity actually decreasing while the breaker is still accelerating.

In the present device three linkages are employed in cascade, the principle of each of the three linkages being the same. Each linkage comprises three elements, a driving link, a connecting link, and a driven link, pivotally connected end-to-end with the outer ends of the linkage turning on fixed pivots, plus a latch mechanism to prevent the toggle from buckling until it is released. In the first of the linkages link used the driving link is the arm I53" of the bell crank already described, the connecting link is link I54, and the driven link is link I55, the outer arm against which the connecting link IEIQ thrusts is small; the result is a mechanical advantage of approximately 12 /2 to l in favor of the latch mechanism which prevents the driven link from rotating.

The latch mechanism in this case is another linkage of the same type, with the driven link of the first linkage forming the driving link of the second and thrusting, at a fairly large angle, against the nearly straight connecting link I58 and driven link I59. The latter forms one arm of a bell crank mounted on a fixed shaft I60 on the frame of the equipment.

The, second arm, I60, of the last mentioned bell crank forms the driving link of a third and similar linkage, which constitutes a latch for the second linkage. This last linkage comprises a .connecting link I$I and a driven link I62 which .turns on a fixed shaft I63. The final driven link extends beyond its pivot on the shaft and is provided with a face I64 which is engaged by a hooked end I65 on a catch or latch member I07 and comprises the final latching element.

It will be seen that in each of the linkages -mentioned the driving link has a relatively large -lever arm with respect to a very small lever arm on the driven link. Each of the driving links is disposed at an angle of approximately 45 With the other two links in their nearly-straightened position, although this angle is not critical. It

'-might appear that a greater advantage could be obtained by making the angle between the driving link and the connecting link approach 90 This is, in fact, the case, but in the 90 position 'the change in lever arm, for a small rotation of the link, is small, while beyond the 45 position it becomes increasingly rapid. The purpose of the entire linkage is to transfer the advantage from a latching mechanism to the driving mechanism as rapidly as possible and this is achieved better by decreasing the lever arm of the driving link simultaneously with the increase of lever arm of the driven link. Moreover, it will be noted that While the driving and driven links are never permitted to straighten fully, the driving and connecting links in each case may pass through the dead center position and it is, in fact, desirable that they do so since this results in minimum total motion of the succeeding linkage. Since the drive is always supplied from the breaker end of the linkage and never from the latch end, the passage of the driving linkage through the dead center position does not result I in any uncertainty or instability of action.

In the linkage which has been shown for illustration the mechanical advantage of the second linkage, when locked, is 8.15 to 1, while that of the third is 9.25 to 1. The overall mechanical advantage of the catch is therefore the product of that of the three linkages taken separately, or I slightly over 942 to l. The multiplication of the inertia of the final link is, however, the square of this, or nearly 890,000 so that an effective mass of one ounce applied at the lever arm of the final link becomes the equivalent of 55,000 pounds added to the mass of the breaker arms themselves. Mechanical advantage due to the linkage is so rapid, however, that by the time the latch face has moved only of an inch when it is released from the hook I65, the mechanical advantage has dropped by a factor of nearly'9 and its inertial effect by a factor of 80. Furthermore, owing to this shift in mechanical advantage the breaker mechanism can accelerate Without any acceleration of the final link and with only moderate accelerations of the intervening links. The result is that in practice circuit breakers may be made to open in of a second or of a cycle where this release mechanism is used, in comparison to a half-cycle or morewhere conventional types of trip are employed.

The release latch IE1 is centrally suspended from a pivot I'II on an arm I13 which, in turn, is pivoted on a shaft I15 on the frame of the apparatus. The end IT! of the latch member which is opposite to the hook I65 is flattened'to form a sear the use of which Will be explained later. A spring I19 attached to a depending arm I on the latch and to a fixed point on the frame tends to rotate the latch around its pivot I'II in a counterclockwise direction, this motion being limited by a fixed pin I3I on the frame. It will be seen that the effect of the spring I19 is to tend to hold the hook I65 in engagement with the latch face ififl of the link I62. A second fixed pin I83 limits the clockwise rotation of the latch.

The tripping mechanism for the breakercomprises a moving-coil type movement which is schematically illustrated as including a permanent magnet I85 having its moving coil I81 connected by a tension link I89 to the pin "I. When the moving coil I0? is excited it raises the lever I73, causing the latch IB'I to rotate against the pin iSI as a fulcrum and disengage the hook IE5 from the face I09, thus releasing the latch. When this has occurred and the excitation is removed from the coil I81 the lever arm I13 carrying the pin III drops. Under these circumstances, however, the end of the hook I65 rests upon a circumferential face formed at the end of the link IISI, so that the latch I61 now pivots around this contact and drops the sear end 'II'I into position to engage the face I93 of a pivoted link I95 and prevent counterclockwise rotation thereof. This serves to lock the dump valve as will be described shortly.

An additional safety trip is provided in addition to the moving-coil type which has just been described. A second lever I91 is pivoted from the pin H5 and extends under the pin I'II, so that when the lever I91 is raised it carries with it the pin, the lever I73, and the latch I61 irrespective of the action of the moving-coil trip. The end of the lever I0? is connected through a link I09 with the plunger 20! of a solenoid, schematically indicated at the reference character 203.

Solenoids of this character are generally used for the trips of devices of the kind described. They have, however, a considerable inductance and hence their operation is not very rapid. The inductance of the moving coil I'8'I can, however, be practically entirely neutralized and therefore their action may be made very fast. Normally (and in every case which has been encountered in practice) the moving coil magnet will trip the breaker a measurable time before-the solenoid can come into action, butin case it should be 13 incapacitated for any reason, the solenoid will back it up and trip the breaker.

Returning now to the link I95, this link is loosely pivoted upon a fixed pin 2B5 mounted on the frame of the device. It is pivotally connected with a long link 2&1, the lower end of which pivots on a fitting 2H fixed to the end of the dump valve push rod I31. The upper end of the link 20? is constrained to move in an arcuate path by a guide crank 2I3 mounted rotatively on a fixed shaft 235 carried by the frame. It will be seen that when the dump valve is seated the linkage consisting of the elements I95, 201, and the push rod I31 is nearly but not quite straight, all of the various toggles comprised in this linkage therefore being broken but barely broken. When the circuit breaker is open the dump valve hook I65 rests on link I62 and the linkage is locked in its position by the engagement of the face I93 with the sear end I11 of the latch until and unless one of the trip coils operates to break this contact, when a sufiicient upward force applied on the push rod will flex the linkage and permit the rod to rise.

We can now trace the operation of the device. The breaker, in the first instance, is in its open position, with the piston 31 at the top of the cylinder 33. The main valve mechanism within the housing @9 is in the position shown, with the passages from the cylinder into the sump completely open so that no pressure can exist within the cylinder other than the normal hydrostatic head of the fluid in the sump. High pressure in the accumulator is, however, at full value of a thousand or more pounds per square inch, being maintained in this condition by the pump P under the control of the pressure-actuated switch. This pressure is available in the pilot valve and is effective both above and below the floating piston I55, tending to hold it against the valve face I83.

To operate the breaker the needle valve I99 is opened, either by hand or by the remote control equipment already described. This relieves the pressure above the piston, offering free egress of the hydraulic fluid through the channel I3I and the tubular dump valve piston I23 into the sump. The pressure below the shoulder on the piston IE5 immediately raises it, opening a direct passage through the connection 93 t the main valve. When this occurs, the piston I being forced up tightly against the block I01, it largely cuts off the flow of hydraulic fluid through this passage.

As soon as the pilot valve opens the full pressure from the source is admitted under the main valve piston 11, lifting it until its reduced upper end enters the bore above it and closes off the passage from the conduit 45 into the sump. At the instant that this occurs the piston strikes the foot 1 5 of the poppet-valve 53 and starts to raise it, this action continuing until the valve face 81 on the piston engages the seat BI and completes the sealing of the exhaust port. As soon as the poppet-valve 63 start to lift the oil pressure from the source is effective through the conduit 45 into the cylinder 33 and forces the piston down until it has reached substantially the bottom of the cylinder. This straightens out the toggles in the latch mechanism until the hook IE5 of the latch I61 drops, simultaneously locking the circuit breaker closed and releasing the end I11 of the latch from the push rod mechanism which holds the dump valve closed. Since at the instant of opening the latch link I 62 loses acceleration rapidly, at the instant of closing it gains acceleration with equal rapidity, and a spring stop 2I1 is therefore provided to absorb the shock of its final closing and prevent snapping past dead center.

It may be noted here that because of the large magnitude of the forces acting uponthe piston the closing action is quite violent and might be destructive were not some means provided of cushioning the final movement. Such a cushion effect can be provided by a projecting tapered end 220 on the piston 31 which projects through a ring 22 I, the ring being held in place by a cylinder head 223 secured to the lower end of the cylinder. The internal periphery of the ring 22I is dimensioned so that when the breaker is nearly closed there is a very small clearance between the ring and the larger end of the taper. When the breaker is open, however, and the small end of the taper lies within the ring there is a wide oil passage provided. As the breaker closes there is therefore a continually increasing dash pot action as the channel between the taper and the ring is constricted, and the final closing of the breaker is fairly gentle. When the breaker trips, however, the ring 22I rises with the piston, permitting oil to flow around the ring and through a plurality of ports 225 and 221 into the cylinder.

As soon as the latch I61 engages with the link IBI the sear end I11 disengages from the link I95, thus releasing the lock on the dump valve. Pressure through the channel I28 then becomes effective to raise the dump valve piston, opening a free passage from below the main valve through the connections 93, 91, and 9 into the sump. The pressure below the main valve piston being released, the'direct pressure from the source, acting through the poppet-valve on the smaller diameter above the piston 11, becomes effective to force it down, the flow of liquid from beneath it continuing to hold the dump valve open. As soon as the poppet-valve has closed the passage between conduits 45 and 5| opens, relieving the pressure within the main cylinder 33, but the motion of the piston 11 continues until it has bottomed due to the continued flow of liquid through the hollow stem of. the poppet-'- valve into the recess in the piston head.

In the meantime, however, the pilot valve has closed, its piston I05 dropping under its own weight, the pressure drop through the valve below it and the increasing pressure of liquid above it. This will occur whether or not the needle valve I01 has been closed in the meantime, since as soon as the dump valve rises its flange I29 will have risen into the cylinder above it to cut of the flow through the tubular dump valve pis- In case an attempt is made to close the breaker upon a fault the trip coil will raise the lever I13 and the latch I61 will pivot around its hooked end to release the contact between the face I93 and the end I11 of the latch, permitting the dump valve to lift. The effect is then the same as that already described at the end of the normal closing operation; the pressure on the main valve piston is immediately relieved into the sump and as the main latch I65 is not engaged the main breaker spring opens the breaker in the same manner as though no attempt was being made to close it. As soon as the dump valve opens the pilot valve closes, as has already been described. Very little loss of fluid into the sump therefore occurs, so that a one gallon accumulator will effect eight or ten closures even when the accumulator is not replenished by the pump.

force is controlled by a relatively minute and easily releasable restraining force, comprising a driving member through which the operating force is applied, a fixed shaft and a driving link pivoted thereon, a mechanical connection between said driving member and said driving link for rotating the latter upon motion of said driving member, a second fixed shaft, a driven link pivotally mounted thereon, and a connecting link pivotally connecting the free ends of said driving link and said driven link, the distance between said fixed shafts being less than the combined lengths of said links as measured between the pivotal centers thereof and so disposed that when said driving member is in its restrained position there is a material angle between said driving link and said connecting link and nearly but not quite a straight angle between said connecting link and said driven link while motion of said driven member tends to straighten the connection between said driving and connecting links and thereby buckle further the connection between said connecting and driven links, latch mechanism for preventing such further buckling, and means for releasing said latch mechanism.

2. A release apparatus comprising a plurality of cascaded mechanisms in accordance with claim 1, the driven link of one of said mechanisms comprising the driving link of the second thereof and said connecting and driven links of said second mechanism comprising the latch mechanism of said first mechanism.

3. A release mechanism in accordance with claim 1 wherein said mechanical connection between said driving member and said driving link comprises a pair of compression links pivotally connected together and to said driving member and said driving link, said compression links being substantially alined when said driving member is in its restrained position and flexing through an increasing angle when released.

4. Release mechanism in accordance with claim 1 wherein said latch mechanism comprises a pair of pivotally connected compression links, one whereof is pivoted at the junction of said driving and connecting links, a fixed shaft whereon the other of said compression links is pivoted, said shaft being so positioned that said compression links also form a nearly but not quite straight angle when said driving member is in its restrained position, a hook member engaging one of said links to hold said links from buckling, and

a trip coil connected to said hook to release the same.

5. A release mechanism for circuit breakers and the like wherein a relatively large operating force is controlled by a relatively minute and easily releasable restraining force, comprising the combination with an operating element of a cascade of toggle linkages each including a pair of links which form a nearly straight angle when said mechanism is in its unreleased condition, said pairs of links being so positioned that none thereof can pass through a straight angle and that buckling of any one pair requires buckling of all of said said pairs, driving connections from said operating element to said cascade of link-- ages, means for restraining the last of said pairs of links in said cascade from buckling, and means for releasing said restraining means.

6. Mechanism in accordance with claim 5 wherein said releasing means comprises a magnetic circuit having an air-gap therein, a coil moveable within said air-gap and connected to said restraining means, and a coil within said air-gap for efiectively neutralizing the inductance of said moveable coil.

'7. Mechanism in accordance with claim 6 including a circuit having relatively high inductance and low resistance connected in parallel with said moveable coil and. a current limiting resistor connected in series with said coil and circuit.

8. Mechanism in accordance with claim 7 wherein said high inductance circuit comprises a magnet having an armature connected to said release and said restraining means.

DONALD M. UMPI-IREY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,138,754 Harris May 11, 1915 1,715,684 Thomas June 4, 1929 1,889,479 Keller Nov. 29, 1932 2,372,140 Van Sickle Mar. 20, 1945 2,544,519 Wood Mar. 6, 1951 FOREIGN PATENTS Number Country Date 246,892 Germany Aug. 29, 1909 

